1. Field of the Invention
The present invention relates it a terminal structure for a surface mount electronic part provided with external terminals to be soldered to lands formed on a printed wiring board;projecting laterally,such as a connector for a PC card.
2. Description of the Related Art
The external terminals of most surface mount electronic parts,to be soldered to soldering lands formed on a printed wiring board,such as connectors for PC cards,have narrow width and are arranged at small pitches. Therefore,the terminals embedded in a synthetic resin so as to project laterally must be arrange in a high positional accuracy.
Referring to FIG. 3 typically showing a conventional terminal structure for an electronic part, base portions of external terminals 2 of an electronic part 1 are fixedly inserted in a housing 3 by press-fitting or embedded in the housing 3 by insert molding. A portion of each external terminal 2 projecting laterally from the housing 3 is bent to form a foot portion so that the foot portion is placed in a predetermined portion on a predetermined soldering land 5 of a printed wiring board 4 when mounting the electronic part 1 on the printed wiring board 4. The foot portion of the terminal 2 is bonded to the soldering land 5 by a solder fillet 6. When mounting the electronic part 1 on the printed wiring board 4, the foot portion of each terminal 2 is placed on the soldering land 5 coated with a soldering cream, and then the soldering cream is melted in a reflow furnace to bond the terminals 2 electrically and mechanically to the corresponding soldering lands 5 with the solder fillets 6.
Another conventional terminal structure shown in FIG. 4 has terminals 2 projecting from a housing, and terminal holders 7 put on the housing to hold and position the terminals 2. The end portions of the terminals 2 are bent substantially at right angles by the bottoms of the terminal holders 7 so that the end position of the terminal 2 to be soldered to soldering lands 5 formed on a printed wiring board 4 extend laterally from the terminal holders 7 and are positioned accurately.
However,it is not easy to form the terminals 2 of the conventional terminal structure shown in FIG. 3 in a high accuracy by a bending process,and the foot portions of the terminals 2 are liable to be dislocated in the direction of the thickness or the width thereof. Consequently, the foot portions of the terminals 2 are arranged in a low positional accuracy and the low positional accuracy of the foot portions of the terminals 2 is liable to cause faulty soldering when mounting the electronic part 1 on the printed wiring board 4. Since each terminal 2 must be projected from the housing 3 by a length long enough to prevent hindrance to forming the terminal 2. Therefore, the terminals 2 projecting in a free state from the housing 3 are liable to be distorted during transportation. Furthermore, the molten solder is sucked upward to and upper portion (high-temperature portion) of the terminal 2 by wicking and an insufficient quantity of solder is available for soldering.
The end portions of the terminals 2 of the conventional terminal structure shown in FIG. 4 are less possible to be dislocated in the direction of the width, the terminals 2 have strength high enough to resist distortion, and the terminals 2 avoid wicking. However, since the terminal holders 7 overlie the soldering lands 5, the terminal holders 7 hinder the visual inspection of the soldered terminals 2. Therefore, it is difficult to handle the electronic part and the reliability of soldering of the terminals 2 to the printed wiring board 4 is deteriorated. Since the end portions of the terminals 2 projection laterally from the terminal holders 7 are liable to slope in different inclinations, the end portions of the terminals 2 are liable to be dislocated in the direction of the thickness of the terminals 2 which often causes faulty soldering.